1. Field of the Invention
The present invention relates to a position sensor printed circuit board (PCB) mounting structure for a commutatorless electric motor, and in particular, to an improved position sensor PCB mounting structure for a commutatorless motor in which the sensing ability of a position sensor is enhanced, an easy operation of the motor is obtained and the service life of the motor is increased by making the replacement of a sensor PCB provided inside the motor easy and which has the benefit of improving a mounting structure of the sensor PCB and the position sensor.
2. Description of the Prior Art
As shown in FIG. 1, in a the conventional commutatorless motor, a stator 1 is disposed at both walls of a casing 4 which forms the outer housing of a motor.
On the peripheral surface of the stator 1, coils are wound, and when power is applied to these coils, a magnetic force is generated.
Inside the stator 1, a rotor 2 rotated by the magnetic force of the stator 1 is disposed spaced from the stator 2, and at a central portion of the rotor, an armature shaft 3 rotating together with the rotor 2 is provided.
At the ends of the armature shaft 3, bearings 6 are disposed for smoothly rotating the armature shaft 3, and on the peripheral surface of the rotor 2, a plurality of permanent magnets 5 having magnetic poles arranged at regular intervals from each other are provided.
And, at one portion inside the casing 4, a sensing unit 300 is fixedly installed for sensing the rotation of the motor by detecting the position of the rotor 2 and supplying the sensed position information to a driving circuit for applying power to the stator 1.
Now, the construction of the sensing unit 300 will be described in detail.
As shown in FIGS. 2 and 3, a sensor printed circuit board (PCB) 11 is provided at one end of a sensor housing 12 mounted to the casing 4 with fastening screws 13, and is fixed by a PCB fastening screw 10.
And, a plurality of position sensors 8 for sensing the position of the magnetic poles of the rotor 2 and supplying the sensing information to the driving circuit for sequentially applying power to the coils of the stator 1, are mounted on the upper surface of the sensor PCB 11.
Here, the position sensors 8, as shown in FIG. 3, are disposed to have a mutually equal spacing on the surface of the sensor PCB 11 having a semicircumferential shape, and the leg 9 of each position sensor 8 is mounted to the sensor PCB 11 through soldering. A through hole type of leg 9 is used.
The sensor PCB arrangement of the conventional commutatorless motor will now be described in detail.
When the motor is driven, as shown in FIG. 1, the sensing unit 300 locates the position of the rotating rotor 2, and based upon the sensed position the driving circuit applies power sequentially to the stator coils, resulting in the generating of torque in the motor.
Here, in the radial direction, the position sensors 8 in the sensing unit 300 are positioned to have a distance of 12 mm from the inside of the permanent magnets 5 disposed in the shape of a hollow circular cylinder and having their magnetic poles equally divided, and in the axial direction of the armature shaft 3, as shown in FIG. 1, the position sensor 8 is positioned where the permanent magnets 5 axially protrude from the rotor 2.
Therefore, a signal is generated in each position sensor 8 as the magnetic flux from the permanent magnets 5 of the rotor 2 passes through the position sensor 8, and this signal generates a pulse signal through the driving circuit on the sensor PCB.
Here, since the position sensor 8 locates the position relative to the circumferential direction of the stator 1, the pulse signal locates the position of the rotor 2 relative to the stator 1.
That is, by using the position signal of the rotor 2 outputted from the position sensor 8, power is applied to each phase of the stator coil 1, but, the circumferential angle between the position sensor 8 and the stator 1 must be accurately set to generate the pulse signal at the correct point.
However, since the conventional commutatorless motor has a construction in which the sensing unit is installed inside the casing, it is difficult to place the position sensor installed in the sensing unit at the correct position when assembling the motor, and as a result there can occur much error.
Further, since the sensor housing must be provided, the material cost is high, and since the position sensor is mounted on the sensor PCB in the shape of cantilever beams, the position signals generated from the position sensors can be distorted due to the vibration of the position sensors caused by the rotation of the motor, consequently causing the motor to be abnormally operated.
In addition, when the motor is used for a long time, since the soldering mounting the position sensors to the sensor PCB is apt to fall off due to the vibration, the position sensors can become detached from the sensor PCB, resulting in the shortening of the life of the position sensor.